Integrative biogeographic studies of the species of Hyalella have not yet been conducted. Here we undertake a preliminary track analysis of the South American species of this genus to improve current understanding of their patterns of geographical distribution.

Coordinates of localities were obtained from the literature or calculated on maps and rounded to minutes. Within each country, localities are ordered roughly in a south-north direction. For details on the localities of each species see Appendix.

The panbiogeographic approach involves plotting distributions of different taxa on maps and joining their separate localities with lines called individual tracks. These tracks represent the geographical coordinates of species or higher taxa. Operationally, they consist of lines drawn on a map connecting the localities at which the taxa occur according to their geographical proximity. When different individual tracks are superimposed, the resulting summary lines are considered generalized tracks, which are interpreted as indicating the pre-existence of ancestral biotas that subsequently became fragmented by tectonic and/or climatic change. If two or more generalized tracks intersect in a given area, they determine a node, which indicates that different ancestral biotic and geological fragments interrelate in space and time as a consequence of terrain collision, docking or suturing. This node thus constitutes a composite area. For further details about panbiogeographic methods, see Morrone (2004, 2006, 2009).

One node (Fig. 9) was found where generalized tracks 1, 2, and 3 intersect, at lake Titicaca.

DISCUSSION

The generalized tracks identified are similar to those described by Menu-Marque et al. (2000), who applied this procedure to the copepod genus Boeckella. That study identified a generalized track in southern Patagonia, the Atlantic coast of Argentina, the Andean mountains of northern Argentina and Chile, and the Andean regions of Bolivia, Colombia and Ecuador. Nevertheless, the nodes reported in the present study differ from those identified by Menu-Marque et al. (2000). Species of Hyalella are also known from Mexico and Central America, Bousfield (1996) supported it, and suggested the presence of Austrohyalella and Mesohyalella genus in South America. Nevertheless, the recent literature mentioned the presence of Hyalella genus for all American continent (Vainola et al., 2008; Witt & Hebert 2000; Wit et al., 2006)

The absence of nodes in southern Patagonia agrees with analyses for Subantarctic islands (Pugh et al. 2002) and southern South America (Dos Santos et al. 2008), about similarities between continental Subantarctic species. Our results contrast with those from calanoid copepods (Menu-Marque et al. 2000) and fishes of the genus Galaxias (Cussac et al. 2004), that are known from southern Patagonia, New Zealand and adjacent islands, a different situation was reported for species of Hyalella that are widespread in South North America (Witt & Hebert, 2000; Witt et al. 2003). The results of geographical distribution of Hyalella genus are similar in comparison to freshwater crabs of Aegla genus that is located in central and southern Argentina and Chile, and east South America, specifically Brazil and Uruguay (Pérez-Lozada et al., 2002, 2004, 2009). Nevertheless, species reports for practically all South American inland waters are rather scarce, so future analyses may modify these results, specifically between 18-8° N, the Titicaca basin, and eastern South America.

ACKNOWLEDGEMENTS

The present study was funded by projects DGI-CDA-2007-01 and MECESUP Project UCT 0804. The authors recognize the contributions of Luciano Parra to the preparation of the present manuscript.

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